Method and device for processing waste having a calorific value

ABSTRACT

A thermal method for continuously processing waste having a calorific value and any degree of moisture, wherein waste is put in a flow of hot, heat-resistant, heat-exchanging material which is warmer than 100° C. The heat exchanging material cools due to heat exchange, the waste dries and the non-evaporated waste components are heated. The cooled, heat-exchanging material is subsequently separated from the dried waste materials and the separated dried waste material is mixed with a percentage of the separated heat-exchanging material. The dried waste material and heat-exchanging material mixture is subsequently heated to pyrolyze waste material and heat the heat exchanging material in preparation for its subsequently use in the continuous process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for processing waste having acalorific value and any degree of humidity.

2. Discussion of Technology

The general process involved in this invention comprises a thermaltreatment, wherein waste is put in a flow of hot, heat-resistant,heat-exchanging material which is warmer than 100° C. The material coolsdue to heat exchange, the waste dries and the non-evaporated wastecomponents are heated. The cooled, heat-exchanging material issubsequently separated from the dried waste material, and at least apart of the separated dried waste material is mixed with a percentage ofthe separated heat-exchanging material. The dried waste material andheat-exchanging material mixture is subsequently heated, and the driedwaste material is pyrolyzed, resulting in its final burning. Theheat-exchanging material is thus heated before further use in thethermal treatment.

More particularly, the invention relates to the processing of somewhatviscous waste containing organic material, including solids and/orliquids. For example, waste of animal origin, waste fromslaughterhouses, sludge from the cellulose and paper industry, rancidoils, etc. or waste containing combustible mineral components may beprocessed using the method. The largest size of the solid wasteparticles is preferably smaller than 5 mm.

A method of the above-mentioned type is described in U.S. Pat. No.4,248,164. According to this method, the fresh waste is dried using hotsand. The dried waste and the cooled sand are removed together from thedrying installation and are separated. The separated dried waste issubjected to a pyrolysis, usually with the help of burners, in acombustion chamber. The separated sand is heated by the gases of thepyrolysis before being supplied to the drying installation. All of thesand which is used for the drying is recycled and supplied back to saiddrying installation at a temperature between 427° and 649° C.(800°-1200° F.).

When the hot sand makes contact with fresh, cold waste, the very greatthermal shock causes the sand grains to burst. Because sand is used, theheat-exchange capability is limited. The high temperature in the dryinginstallation limits the life of the drying installation unless it ismade of special materials, which makes this process expensive.

GB-A-160,422 describes a method for drying material which needs to beground in a revolving drum. The grinding elements (balls) from the drumare collected and are carried back into the drum via a tube in whichthey are heated by a furnace. However, the material is not waste and isnot pyrolyzed after the drying.

The present invention aims to remedy said disadvantages and to provide amethod for processing waste having a calorific value which has a highthermal efficiency and a maximum utilization of the processed waste. Thepresent invention also aims to provide a method which is ecologicallysound and can be realized with a relatively inexpensive device having along life.

SUMMARY OF THE INVENTION

In reaching this aim according to the invention, a granulated materialused as heat-exchanging material is heated. Fresh waste material isintroduced into the flow of the heated granulated material, therebydrying the waste material. The dried waste material and granulatedmaterial are then separated. The dried waste material separated from thegranulated material is mixed with only a part of the separated, cooledgranulated material. This first mixture is pyrolyzed. The remaining partof the separated, cooled granulated material is mixed with thegranulated material heated by the pyrolysis. This second mixture is usedto dry fresh waste.

Preferably, the dried waste material and the granulated material aresubstantially separated from one another by collecting them separatelyafter the drying.

Preferably, all the separated dried waste material is mixed with only apart of the separated granulated material.

In order to further diminish the thermal shock to the granulatedmaterial, it is recommended to preheat the waste before introductioninto the flow of the heated granulated material. For example, freshwaste may be preheated through heat exchange using steam released aspreviously introduced waste is dried.

The present invention also contemplates a device for processing wastehaving a calorific value and any degree of humidity. The device includesa horizontal drying installation having a drying compartment. A wastesupply pipe supplies fresh waste to the drying compartment. A heatinginstallation for pyrolzing dried waste material and heating granulatedmaterial supplies pyrolyzed waste material and heated granulatedmaterial to the drying installation through a conveyor outlet pipe.Means for collecting dried waste material and granulated material fromthe drying compartment collect each material substantially separately. Afirst supplying means supplies at least part of the dried waste materialand at least part of the granulated material from the collecting meansto the heating installation. A second supplying means supplies at leastpart of the granulated material from the collecting means to theconveyor outlet pipe.

Preferably, the drying installation contains an ash removal compartmentarranged such that ashes produced during the pyrolysis of the wastematerial are removed from the granulated material before reaching thedrying compartment. The removal may be via openings in a drum wall.

The heating installation includes an inner cylinder which is coaxialwith an outer cylinder. The cylinders define an interspace for receivingthe dried waste material and the granulated material from the firstsupplying means. A chamber surrounds both cylinders. The chambercommunicates with an incinerator and a heat exchanger.

BRIEF DESCRIPTION OF THE DRAWING

In order to better explain the characteristics of the invention, thefollowing preferred embodiment of a method and a device for processingwaste having a calorific value is given as an example and without beinglimitative in any way, reference being made to the accompanying drawing,in which:

FIG. 1 shows a schematic, partially sectioned view of a waste processingdevice according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The figure shows a device for processing industrial sludge, for example,with 10% dry components having a calorific value of some MJ/kg, forexample 15 MJ/kg.

The device contains a reservoir 1 for storing the waste material to beprocessed, a drying installation 2 with which reservoir 1 is connected,and a heating installation 3 which is connected to drying installation 2for heating granulated material 4. An incinerator 5 and a heat exchanger45 are connected to heating installation 3. Granulated material 4consists of heat-resistant granules which are resistant to temperaturesrequired for the pyrolysis of the waste, preferably to temperaturesabove 850° C., and which have a high thermal conductivity.

The granulated material preferably consists of ceramic material.Suitable materials are, for example, burnt clay or calcium aluminatewith an aluminum alloy that depends on the temperature. The radiationcapacity of such materials is usually about 201 2/M². °K. h.

The size of the grains is, for example, such that they are detained by asieve with meshes of 9×9 mm, but can pass through a sieve with meshes of11×11 mm.

The specific surface of the grains must be as large as possible. Forgrains made of the above-mentioned materials and with theabove-mentioned size, this specific surface is about 750 m² /m³.

Drying installation 2 has the shape of a horizontal, slightly inclineddrum dryer which contains an actual drum 6 which is mounted rotatableabout its axis surrounded by a thermally and acoustically insulatingjacket 7. Drum 6 is divided into five compartments by internalring-shaped partitions 8, 9, 10 and 11. Seen from the most elevated endof drum 6, sequentially these compartments are a homogenizationcompartment 12, an ash removal compartment 13, a drying compartment 14,a separation compartment 15 for separating out the dried wastecomponents and a granulated material discharge compartment 16.

Reservoir 1 connects to drying compartment 14 via a waste pipe 17 and awaste supply pipe 18. The wall of drum 6 is provided with openings atthe height of ash removal compartment 13, so that it forms a sievethrough which ashes, but not granulated material 4, pass. In order tocollect the ashes, an ash funnel 19 is mounted under this wall sectionof the drum.

In an analogous manner, the wall of drum 6 is provided with openings atthe height of separation compartment 15, so that the corresponding wallpart forms a sieve through which dried waste material, but notgranulated material 4, passes. In order to collect the waste material, awaste funnel 20 is mounted under this wall section of the drum.

Granulated material discharge compartment 16 situated at the leastelevated end and is provided with openings 21 through which granulatedmaterial 4 passes. In order to collect the granulated material, agranulated material funnel 22 is mounted under this wall section of thedrum.

A number of air supply lines 23 open into jacket 7. Jacket 7 is providedat its highest point with a steam outlet 24 which connects via a steampipe 25 to a serpentine curve situated in reservoir 1 which forms a heatexchanging pipe 26.

At the most elevated end of drum 6, a conveyor outlet pipe 27 isconnected for supplying granulated material 4. Conveyor outlet pipe 27has an internal conveyor outlet screw 28.

Granulated material funnel 22 is connected via a combined return pipe 29to the top of vertically erected heating installation 3. A liftmechanism, which is not represented in the figure, is mounted insidecombined return pipe 29. Granulated material funnel 22 is also connectedvia a granulated material return pipe 30 to conveyor outlet pipe 27.Another lift mechanism, also not represented in the figure, and a sieve31 are mounted inside granulated material return pipe 30. Waste funnel20 opens into combined return pipe 29. Sieve 31 also opens into combinedreturn pipe 29. Together with partition 11 and the sieve-forming wallparts of drum 6, waste funnel 20 and granulated material funnel 22 formmeans to collect the granulated material and dried waste materialseparately.

Heating installation 3 includes a perforated inner cylinder 32 which iscoaxial with a perforated outer cylinder 33. Cylinders 32 and 33 aresituated vertically in a chamber 34 which is divided into threecompartments 35, 36 and 37 around the outer cylinder 33.

A space 38 inside the inner cylinder 32 is closed at the top and at thebottom. A ring-shaped interspace 39 between cylinders 32 and 33 opens atthe top into a common entry to which combined return pipe 29 isconnected. Interspace 39 opens at the bottom into a conveyor pipe 40.Conveyor pipe 40 has an internal conveyor screw 41 and is connected toconveyor outlet pipe 27.

Top compartment 35 and bottom compartment 37 connect via a heatexchanger return pipe 42 over a first fan 43 to incinerator 5 and over asecond fan 44 to a secondary part of heat exchanger 45. Incinerator 5 isconnected to a primary part of heat exchanger 45. This primary partopens into an outlet 47. The secondary part of heat exchanger 45 isconnected via a heat exchanger supply pipe 48 to middle compartment 36of heating installation 3.

At the end of heat exchanger return pipe 42 which connects toincinerator 5, an open burner 49 is connected.

The above-described device works as follows:

In reservoir 1, a mixture of waste having different calorific values isstored so as to be able to guarantee the heat required for the method.Any solid or liquid waste mixture can be processed by the presentinvention. However, by mixing different sorts of waste, one can makesure that the waste has enough calorific value to supply the heatrequired to preserve the method without requiring any fuel from outsidethe device after start-up. The more solid components the waste contains,the higher the calorific value. In reservoir 1, the waste mixture isheated to about 800° C. by means of heat exchange with the steam whichis generated during the drying of the waste and which flows through heatexchanging pipe 26.

The preheated waste is supplied via waste pipe 17 and waste supply pipe18 to drying compartment 14 of drying installation 2, whose drum 6 iscontinuously rotated. Here, the waste is exposed to hot granulatedmaterial 4 which is moved in drum 6 from the most elevated end to theleast elevated end. This granulated material has a temperature between200°and 300° C., for example a temperature of about 250° C., when itarrives over ring-shaped partition 9 in drying compartment 14.

Due to heat exchange the waste dries, whereby the dried waste materialis heated to 100° C. or more and the granulated material cools topreferably the same temperature. From the mixture of cooled granulatedmaterial and dried waste components which end up in separationcompartment 15 over ring-shaped partition 10, the dried waste materialis separated as it falls through a sieve-forming wall section of drum 6.The waste material is collected in waste funnel 20 and subsequentlysupplied to combined return pipe 29.

Practically only granulated material falls over the overflow formed bysmaller, ringshaped partition 11 into granulated material dischargecompartment 16 from where it falls through openings 21 and intogranulated material funnel 22.

The major part of granulated material 4, normally 75 to 85 wt %, forexample 80 wt %, is directly supplied to conveyor outlet pipe 27 viagranulated material return pipe 30 after it has been purified by removalof waste material using sieve 31. By means of conveyor outlet screw 28,this part of the granulated material is mixed with the mixture of hotgranulated material and ashes coming from heating installation 3 at atemperature of about 750° C. This second mixture is advanced intohomogenization compartment 12, where the mixing continues. Inhomogenization compartment 12, the difference between the temperaturesof the core and the outside of the granules of the granulated materialdrops below 40° K, and the average temperature of the mass of granulatedmaterial is brought between 200° to 300° C., for example to about 250°C. From the homogenous mixture which falls over partition 8 into ashseparation compartment 13, the ashes are removed as they fall throughanother sieve-forming wall section of drum 6. These ashes are collectedin ash funnel 19.

Practically pure granulated material 4 with an average temperature ofabout 250° C. falls over partition 9 into drying compartment 14.

The part of the waste material which is removed from granulated materialreturn pipe 30 by means of sieve 31 is added to the waste material andgranulated material in combined return pipe 29.

A smaller part of granulated material 4, between 15 and 25 wt %, forexample 20%, is supplied through combined return pipe 29 by a liftmechanism, not represented here, after waste material from waste funnel20 and sieve 31 are added, to interspace 39 of heating installation 3.In interspace 39, the mixture of granulated material and waste materialfalls due to the force of gravity.

In the middle zone of interspace 39, heated air at a temperature ofabout 750° C., coming from the secondary part of heat exchanger 45, isintroduced via heat exchanger supply pipe 48 and middle compartment 36.The supplied air flows from middle compartment 36 to the middle zone ofinterspace 39 through cylinders 33 and 32 and thus through the materialtherein. This air causes the pyrolysis and the final burning of thewaste material which is mixed with the granulated material.

Part of the gases coming from the middle zone flows upward in space 38and through the top zone of interspace 39.

The gasification and the first pyrolysis of the waste material takesplace in the top zone of interspace 39, whereby a gaseous fuel isproduced of relatively inferior quality. This gaseous fuel is removedvia top compartment 35 and carried via heat exchanger return pipe 42 bymeans of fans 43 and 44, partly to incinerator 5 and partly to thesecondary part of heat exchanger 45.

Another part of the gases coming from the middle zone flows downward inspace 38 and subsequently through the lower zone of interspace 39. Thefinal combustion of all combustible elements in the waste material takesplace in this lower zone. Also, the temperature variations in thegranulated material are attenuated in this lower zone. The gases fromthis lower zone are collected in bottom compartment 37, from where theyare mainly supplied to incinerator 5 and to a lesser extent to thesecondary part of heat exchanger 45 via heat exchanger return pipe 42 bymeans of fans 43 and 44.

The mixture of granulated material and ashes is removed from the bottomof heating installation 3 and is carried through conveyor pipe 40 toconveyor outlet pipe 27 at a temperature of about 750° C. by means of aconveyor screw 41.

The mixture of gases at about 300° C. from top compartment 35 and theair, 30 to 40% of which is partly polluted by combustion gases from thelower one in interspace 39, at about 750° C. from bottom compartment 37,are burnt in the incinerator 5. Any surplus of these gases is burnt inopen burner 49.

The combustion gases of incinerator 5 at a temperature of about 850° C.are carried via a connection pipe 46 to the primary part of heatexchanger 45 where the air supplied to the middle compartment 36 isheated to about 750° C. Heat exchanger 45 provides the necessarypressure and under pressure for the working of the heating installation3, incinerator 5, and heat exchanger 45 combination as a whole.

In order to start the device, a high-grade fuel is supplied andcombusted in incinerator 5. As soon as the temperature of the granulatedmaterial which is collected from drying installation 2 is higher than100° C., waste is gradually supplied to drying installation 2. As soonas hot granulated material is supplied to drying installation 2 at atemperature of 200° to 250° C., the normal flow of waste can besupplied. In the meantime, the supply of fuel to incinerator 5 isreduced to zero. This starting procedure requires one hour at the most.

The steam which is produced during the drying in drying installation 2and collected via steam outlet 24 can be partly used for preheating thewaste. Any surplus of steam can be efficiently used for heating waterfor domestic use. Depending on the composition, the condensate of thissteam can be chemically neutralized or mixed with 5 vol. % preheated airand heated up to 800° C. in a regeneration heat exchanger, not shown inthe figure, which works uninterruptedly with granulated material. Thethermal agent of the heater is the heater agent itself after a flow ofgaseous fuel has been led through it, coming, for example, from the topzone of heating installation 3. The fuel is burnt and the air isdispersed in the steam mass. During the period in which the steam has ahigh temperature, the oxidizing effect of the air contributes to thedetoxication of the steam.

In order to prevent condensate from forming inside jacket 7, hot air canbe blown through air supply lines 23 in jacket 7. This air can be heatedby heat exchanger 45.

According to the above-described method and with the above-describeddevice, a complete treatment of all harmful materials in the processedwaste is obtained. The potential energy which is stored in the waste isefficiently utilized. Only in the case of waste with a high degree ofhumidity must fuel be added from outside the device. In the case ofrelatively dry waste, for example waste which contains 25% water and hasa heating value of more than 2 MJ/kg, fuel from outside is not evenrequired. Additional fuel is required only when starting or re-startingthe device, but even then the consumption is relatively low. The steamproduced is entirely utilized. The ashes can be directly collected viaash funnel 19 and do not disperse in the gases. The collected ashes havea temperature of only 200° C., which indicates that the considerableheat of these ashes has been fully used in this device.

The intensive heat transfer of the granulated material allows for aninexpensive, compact and very efficient device.

The present invention is by no means limited to the embodimentsdescribed above and represented in the accompanying drawing; on thecontrary, such a method and device for processing waste can be realizedin all sorts of variants while still remaining within the scope of theinvention.

I claim:
 1. A method for processing waste having a calorific value andany degree of humidity, comprising the steps of:heating a granulatedheat-exchanging material and establishing a flow of the heated heatexchanging material; introducing a flow of waste material into the flowof the heated heat exchanging material such that the waste material isheated and dried and the granulated material is cooled; separating thedried waste material and the cooled heat exchanging material; forming afirst mixture of at least part of the dried waste material and a portionof the cooled heating exchanging material; pyrolyzing the first mixturesuch that the dried waste material is burned to ashes and the heatexchanging material is reheated; forming a second mixture of thereheated heat exchanging material and the remaining portion of thecooled heating exchanging material; and feeding the second mixture as aheat-exchanging material into the flow of heat exchanging material todry the flow of waste material in a continuous process.
 2. The methodaccording to claim 1, wherein the dried waste material and the cooledheat exchanging material are substantially separated by collecting themseparately.
 3. The method according to claim 1, including combustinggases released during pyrolysis, and using heat produced from thecombustion for the pyrolyzing.
 4. The method according to claim 1,wherein the first mixture is formed of all of the dried waste materialand only part of the cooled heat exchanging material.
 5. The methodaccording to claim 1, including preheating the waste material beforeintroducing it into the flow of the heated heat exchanging material. 6.The method according to claim 5, wherein the preheating of the wastematerial is carried out by heat exchange with steam released from thedrying of previously introduced waste material.
 7. The method accordingto claim 1, including reheating the heat exchanging material of thefirst mixture during the pyrolysis to 250° to 300° C. such that thesecond mixture is heated to a temperature of 200° to 300° C. 8.Apparatus for processing waste having a calorific value and any degreeof humidity, comprising:a horizontal waste drying installation (2)having a drying compartment (14); a waste supply pipe (18) whichsupplies a flow of fresh waste to the drying compartment (14); a heatinginstallation (3) for receiving dried waste material from the dryinginstallation, for pyrolyzing said dried waste material and for heatingheat exchanging material, the heating installation (3) including aconveyor outlet pipe (27) supplying pyrolyzed waste material and heatedheat exchanging material to the waste drying installation (2) from theheating installation; means for collecting (20, 22) dried waste materialand heat exchanging material substantially separately from the dryingcompartment (14); a first means for supplying (29) at least part of thedried waste material and at least part of the heat exchanging materialfrom the collecting means (20, 22) to the heating installation (3); anda second means for supplying (30) at least part of the heat exchangingmaterial from the collecting means (20, 22) to the conveyor outlet pipe(27) for return to the waste drying installation.
 9. The apparatusaccording to claim 8, further comprising:an incinerator (5) whichreceives and combusts gases released during the pyrolysis in the heatinginstallation (3); and a heat exchanger (45) which uses heat from thecombustion in the incinerator (5) for pyrolyzing dried waste materialand heating heat exchanging material in the heating installation (3).10. The apparatus according to claim 8, further comprising:ahomogenization compartment (12) within the drying installation (2) whichcommunicates between the conveyor outlet pipe (27) and the dryingcompartment (14) and homogeneously mixes the heat exchanging materialsupplied by the second supplying means (30) with the heated heatexchanging material from the heating installation (3).
 11. The apparatusaccording to claim 8, further comprising:an ash removal compartment (13)within the drying installation (2) arranged to remove ashes produced bythe pyrolysis of the waste material from the heat exchanging materialbefore the heat exchanging material reaches the drying compartment (14).12. The apparatus according to claim 8, wherein the drying installationincludes a horizontal drum (6) which is rotatable about its horizontalaxis, the drum (6) being divided into compartments (12, 13, 14, 15, 16)including the drying compartment (14) by internal ring-shaped partitions(8, 9, 10, 11), and a jacket (7) which surrounds the drum (6).
 13. Theapparatus according to claim 12, further comprising:a steam outlet (24)connected to the jacket (7); and a heat-exchanging pipe (26)communicating with the steam outlet (24) such that the waste materialflow is preheated before being supplied to the waste drying compartment(14).
 14. The apparatus according to claim 9, wherein the heatinginstallation (3) is a vertical heating installation comprising:an innercylinder (32) which is coaxial with an outer cylinder (33), therebydefining an interspace (39) which receives the dried waste material andthe heat exchanging material from the first supplying means (29); and achamber (34) which surrounds both cylinders and communicates with theincinerator (5) and the heat-exchanger (45).
 15. The apparatus accordingto claim 14, wherein the chamber (34) is divided into a top compartment(35), a middle compartment (36) and a bottom compartment (37) around theouter cylinder (33), the top compartment (35) and the bottom compartment(37) arranged to supply gases released during the pyrolysis to theincinerator (5) for combustion, and the middle compartment (36) arrangedto receive heat from the heat exchanger (45) for pyrolyzing dried wastematerial and heating heat exchanging material in the heatinginstallation (3).